/**
 * Created with IntelliJ IDEA.
 * Description:求平均数
 * 键盘输入任意多个10000以内正整数（负数代表结束），求出它们的平均数，
 * 输入：12 23 32 43 -1
 * 输出：27.50
 * User: zjc
 * Date: 2022-05-01
 * Time: 20:42
 */
import java.util.Scanner;

public class Project {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        double avg = 0;
        int sum = 0;
        int count = 0;
        while(true){
            int a = scan.nextInt();
            if(a<0){
                break;
            }else{
                sum += a;
                count++;
            }
        }
        avg = (double)sum/count;
        System.out.println(String.format("%.2f",avg));
    }
}
